This invention relates to a heat source used in smoking articles which produce substantially no visible sidestream smoke. More particularly, this invention relates to a carbon containing heat source for a smoking article which provides sufficient heat to release a flavored aerosol from a flavor bed for inhalation by the smoker.
There have been previous attempts to provide a heat source for a smoking article. However, these attempts have not produced a heat source that is satisfactory for use in a smoking article such as described in copending U.S. patent application Ser. No. 07/223,153, filed concurrently herewith and now U.S. Pat. No. 4,991,606.
For example, Siegel U.S. Pat. No. 2,907,686 discloses a charcoal rod having an ash content of between 10% and 20% and a porosity on the order of 50% to 60%. The charcoal rod is coated with a concentrated sugar solution so as to form an impervious layer during burning. It was thought that this layer would contain gases formed during smoking and concentrate the heat thus formed. The charcoal may or may not be activated.
Boyd et al. U.S. Pat. No. 3,943,941 discloses a tobacco substitute which consists of a fuel and at least one volatile substance impregnating the fuel. The fuel consists essentially of combustible, flexible and self-coherent fibers made of a carbonaceous material containing at least 80 percent carbon by weight. The carbon is the product of the controlled pyrolysis of a cellulose based fiber containing only carbon, hydrogen and oxygen, and which has suffered a weight loss of at least 60 percent during the pyrolysis.
Bolt et al. U.S. Pat. No. 4,340,072 discloses an annular fuel rod extruded or molded from tobacco, a tobacco substitute, a mixture of tobacco substitute and carbon, other combustible materials such as wood pulp, straw and heat-treated cellulose or an SCMC and carbon mixture. The wall of the fuel rod is substantially impervious to air.
Banerjee et al. U.S. Pat. No. 4,714,082 discloses a short combustible fuel element having a density greater than 0.5 g/cc. The fuel element disclosed in Banerjee has a plurality of longitudinal passageways in an attempt to maximize the heat transfer to the aerosol generator.
Published European patent application 0 117 355 by Hearn et al. discloses a carbon heat source and a process for making a carbon heat source for a smoking article. The carbon heat source is formed from pyrolized tobacco or other carbonaceous material and is in the shape of a tube. The process for making the carbon heat source comprises three steps: a pyrolysis step, a controlled cooling step and either an oxygen absorption step, a water desorption step or a salt impregnation and subsequent heat treatment step.
Published European patent application 0 236 992 by Farrier et al. discloses a carbon fuel element and process for producing the carbon fuel element. The carbon fuel element disclosed contains carbon powder, a binder and other additional ingredients as desired and is formed with one or more longitudinally extending passageways. The carbon fuel element is produced by pyrolizing a carbon containing starting material in a non-oxidizing atmosphere, cooling the pyrolized material in a non-oxidizing atmosphere, grinding the pyrolized material, adding binder to the ground material to form the fuel element and pyrolizing the formed fuel element in a nonoxidizing atmosphere. A heating step may be performed on the ground material after grinding.
Published European patent application 0 245 732 by White et al. discloses a dual burn rate fuel element which utilizes a fast burning segment and a slow burning segment.
All of these heat sources are deficient because they provide unsatisfactory heat transfer to the flavor bed resulting in an unsatisfactory smoking article, i.e., one which fails to simulate the flavor, feel and number of puffs of a conventional cigarette.
It would be desirable to provide a carbonaceous heat source that will maximize heat transfer to the flavor bed.
It also would be desirable to provide a heat source that undergoes substantially complete combustion leaving minimal residual ash.
It still further would be desirable to provide a heat source that will ignite under normal lighting conditions for a conventional cigarette.